Sheet peripheral edge grinder

ABSTRACT

A polishing machine for polishing a periphery of a sheet of the present invention comprises a grinding shaft tilting mechanism ( 1 ) capable of changing a tilting angle of a rotary shaft of a grinding stone ( 3 ) with respect to a rotary shaft of the sheet ( 2 ) and also capable of changing its tilting direction. Accordingly, in a recess portion or a protrusion portion in the periphery, when the tilting direction is changed while the tilting angle is being maintained, chamfering (polishing) can be executed with high accuracy in the same manner as that of the outer circumferential portion of the sheet.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field of the Invention

[0002] The present invention relates to a polishing machine forpolishing a periphery of a sheet when a rotating grinding stone is madeto come into contact with a periphery of a rotating sheet. Moreparticularly, the present invention relates to a polishing machine forpolishing a periphery of a sheet suitably used for polishing a peripheryof a sheet such as a semiconductor wafer, in the periphery of which anotch or orientation-flat marking is formed.

[0003] 2. Background Art

[0004] A surface of a semiconductor wafer, which has been cut off bymeans of slicing, is polished, and a periphery of the semiconductorwafer is also polished in order to prevent the occurrence of cracks andthe adhesion of dust. In this case, the periphery of the semiconductorwafer is polished in such a manner that an oblique face of a rotatinggrinding stone having grooves is pressed against the rotatingsemiconductor wafer so that a rotary shaft of the semiconductor waferand that of the grinding stone can be parallel with each other.

[0005] However, in the above conventional method of polishing theperiphery of the semiconductor wafer, as the abrasive grains move onlyin the circumferential direction of the semiconductor wafer, stripes areformed on the polished face in the periphery of the semiconductor waferby partial blades of the grinding stone, that is, it is impossible toprovide a polished face, the surface roughness accuracy of which issufficiently high. When the surface roughness accuracy of the polishedface of the periphery is insufficient as described above, the followingproblems may be encountered. A surface of the periphery is locallycracked and chips are generated from the cracks. Accordingly, dustadheres onto the surface of the periphery. Further, fine powder getsinto the cracks, which could be a cause of generating dust. Furthermore,cleaning water staying in the cracks is vaporized in a later process,which has a bad effect on the after-process of manufacturing the wafer.In order to solve the above problems, the following countermeasures aretaken. The grain size of the grinding stone is reduced to be moreminute, the quantity of cutting is decreased, the number of times ofdressing is increased, or the surface roughness accuracy of the polishedface is enhanced by changing over several grinding stones (Two stages ofgrinding stones or three stages of grinding stones are used.). However,the effects provided by the above countermeasures are limited. Further,when the above countermeasures are adopted, the grinding efficiency isdeteriorated.

[0006] Therefore, the present applicant has proposed the followingtechnique which is disclosed in Japanese Examined Patent Publication No.2876572. While a rotary shaft of a grinding stone is being tilted in thetangential direction of an outer circumference of a semiconductor wafer,a peripheral edge of the semiconductor wafer is polished. Due to theforegoing, a direction of the motion of abrasive grains of the grindingstone is tilted with respect to a polished face of the semiconductorwafer, and the occurrence of stripes on the polished face caused bypartial blades of the grinding stone can be prevented. As a result,polishing can be executed with high accuracy.

[0007] However, the above polishing method is disadvantageous asfollows. According to the above polishing method, the rotary shaft ofthe grinding stone can be tilted only in one direction. Therefore, whenthe semiconductor has a notch portion or orientation-flat markingportion, it is impossible to successfully polish the peripheral edge ofthe notch portion or orientation-flat marking portion.

SUMMARY OF THE INVENTION

[0008] In view of the above problems, it is an object of the presentinvention to provide a polishing machine for polishing a periphery of asheet capable of accurately polishing the peripheral edge of the sheetincluding a recess portion and protrusion portion even when polishing isconducted on a sheet such as a semiconductor wafer, the peripheral edgeof which has a recess portion or protrusion portion such as a notchportion or orientation-flat marking portion.

[0009] An embodiment of the polishing machine for polishing a peripheryof a sheet of the present invention comprises a grinding stone shafttilting mechanism, the tilting angle of the rotary shaft of the grindingstone of which can be changed in the tangential direction of theperipheral edge of the sheet, and the direction of tilting of which canbe also changed. By the above grinding stone shaft tilting mechanism,the recess portion and the protrusion portion of the peripheral edge ofthe sheet can be polished with high accuracy.

[0010] According to another embodiment of the polishing machine forpolishing a periphery of a sheet of the present invention, when thetilting angle of the grinding stone is adjusted according to achamfering angle of the sheet, the peripheral edge of the sheet can beeffectively and accurately polished.

[0011] According to still another embodiment of the polishing machinefor polishing a periphery of a sheet of the present invention, when therecess portion or the protrusion portion of the peripheral edge of thesheet is polished, it is prescribed that a tilting direction of therotary shaft of the grinding stone is adjusted according to the rotaryangle of the sheet. Therefore, it is possible to polish the periphery inthe recess portion and the protrusion portion with high accuracy.

[0012] According to still another embodiment of the polishing machinefor polishing a periphery of a sheet of the present invention, it isprescribed that polishing is conducted at a bottom of the recess portionof the peripheral edge of the sheet while the tilting angle of thegrinding stone is being kept at 0°.

[0013] According to still another embodiment of the polishing machinefor polishing a periphery of a sheet of the present invention, it isprescribed that a polishing face of the grinding stone is formed into aface, the angle of which is the same as that of an oblique face angle ofgrinding stone grooves which are self-formed according to the tiltingangle of the grinding stone having grooves. Since the face, the angle ofwhich is the same as that of the oblique face of the grinding stonegrooves is self-formed according to the tilting angle of the grindingstone, the number of the acting abrasive grains is increased, and theabrasive grains act uniformly. Therefore, the surface accuracy of thepolished face can be enhanced.

[0014] According to still another embodiment of the polishing machinefor polishing a periphery of a sheet of the present invention, agrinding stone, the degree of bonding of which is lower than that of themetal bond, is used. Therefore, the abrasive grains easily come off whenan over-load is given to them, and the polished face can be preventedfrom being damaged.

[0015] According to still another embodiment of the polishing machinefor polishing a periphery of a sheet of the present invention, it isrestricted that the sheet is a semiconductor wafer and the recessportion is a notch portion or an orientation-flat portion.

[0016] The present invention will become more apparent from thefollowing descriptions of the preferred embodiments with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a side view showing an outline of a grinding stonetilting mechanism used for a polishing machine for polishing a peripheryof a sheet according to an embodiment of the present invention.

[0018]FIG. 2 is a plan view showing an outline of the grinding stonetilting mechanism shown in FIG. 1.

[0019]FIG. 3 is an enlarged sectional view of a grinding stone sectionfixed to a spindle.

[0020]FIGS. 4A to 4E are schematic illustrations for explaining apolishing process of polishing a notch portion conducted by a polishingmachine for polishing a periphery of a sheet of the present invention.

[0021]FIGS. 5A and 5B are views showing a spherical linear motor bearingwhich is another embodiment used for the grinding stone tiltingmechanism, wherein FIG. 5A is a side view showing an outline of thespherical linear motor bearing, and FIG. 5B is a plan view showing anoutline of the spherical linear motor bearing.

THE MOST PREFERRED EMBODIMENT

[0022] Referring to the accompanying drawings, an embodiment of thepolishing machine for polishing a periphery of a sheet of the presentinvention will be explained as follows. FIG. 1 is a side view of thegrinding stone tilting mechanism 1 of the polishing machine forpolishing a periphery of a sheet of the present invention, and FIG. 2 isa plan view. The grinding section 3 for polishing the semiconductorwafer 2, which is a sheet, is fixed to the spindle 4 by means ofscrewing. The spindle 4 is rotated by a rotation drive mechanism notshown. The spindle 4 is pivotally supported by the slider 5 at aposition distant from the grinding section 3 by, for example, distanceL. Further, the spindle 4 is pivotally supported by the arm 6 at aposition distant from the grinding section 3 by, for example, distance2L.

[0023] In the slider 5, the first linear bearings 51, 52, the number ofwhich is two, are arranged at an interval in the linear direction. Whenthese linear bearings are put on the guide rail 71 on the mount 7, theslider 5 can be linearly slid with respect to the mount 7. The motor 9is arranged on the mount 7, and the slider 5 and the arm 6 are engagedwith the screw member 8 which is driven by this motor 9. The screwmember 8 is composed of a screw portion 8 a, the pitch of which is 1.0,and a screw portion 8 b, the pitch of which is 2.0. This screw portion 8a is meshed with the first nut member 53 which goes ahead and back whenthe screw member 8 is rotated. This nut member 53 is connected with theslider 5. The other screw portion 8 b is meshed with the second nutmember 61 which goes ahead and back when the screw member 8 is rotated.The arm 6 is pivotally connected with this second nut member 61. Thesecond nut member 61 has the second linear bearing 62. This linearbearing 62 is put on the guide rail 71, which is arranged on the mount7, so that the linear bearing 62 can be linearly slid. Accordingly, whenthe motor 9 is driven, the first linear bearings 51, 52 and the secondlinear bearing 62 linearly slide on the guide rail 71, so that thetilting angle of the spindle 4 in the axial direction can be changed.

[0024] A pitch ratio of the two screw portions 8 a and 8 b of the screwmember 8 is set at 1:2. The reason is described as follows. A supportpoint, at which the slider 5 supports the spindle 4, is distant from thegrinding stone section 3 by distance L, and a support point, at whichthe arm 6 supports the spindle 4, is distant from the grinding stonesection 3 by distance 2L, that is, the ratio is 1:2. Therefore, it isnecessary for the pitch ratio of the two screw portions 8 a and 8 b ofthe screw member 8 to agree with this ratio. This pitch ratio must bechanged according to the ratio of the distances of these support points.In the above embodiment, the slider 5 and arm 6 are moved by one motor,however, independent screw members, the pitches of which are differentfrom each other, may be respectively driven by different motors.

[0025] According to the grinding stone tilting mechanism of the presentinvention, it is possible to change a tilting direction of the grindingshaft. At a lower portion of the mount 7, there is provided an arcuatecurvature type bearing 72. When this arcuate curvature type bearing 72is put on an arcuate guide rail 10, it is possible for the mount 7 to bemoved in an arc. When this mount 7 is moved in an arc, an appropriatelink mechanism or screw mechanism not shown is used. As described above,according to the grinding stone tilting mechanism of the presentinvention, both the tilting angle and the tilting direction can bechanged.

[0026]FIG. 3 is a partially enlarged view showing the grinding stonesection 3 which is attached to the spindle 4 by means of screwing. Thegrinding stone section 3 includes: a bastard grinding stone portion 3 a;a smooth grinding stone portion 3 b; and an attaching portion 3 c. Aring-shaped groove 31 is formed around the grinding stone. As shown inthe enlarged view, the inclined portion 31 a and bottom portion 31 b ofthe groove 31 are used as a polishing face of the grinding stone. Thisinclined portion 31 a polishes the chamfered face 2 a in the peripheraledge of the semiconductor wafer 2, and the bottom portion 31 b of thegroove 31 polishes the outer circumferential face 2 b of the wafer 2. Inthis polishing process, an oblique face, the angle of which is the sameas that of the oblique face of the grinding stone groove, is self-formedaccording to the tilting angle of the girding stone. Therefore, not onlya portion of the oblique face but also the entire oblique face can beeffectively utilized for polishing, and the number of acting abrasivegrains of the grinding stone is increased. Accordingly, the actingabrasive grains can act uniformly on the polished face, and the face canbe polished with high accuracy. In this connection, in this embodiment,the grinding stone section 3 includes two types of a bastard grindingstone portion and a smooth grinding stone portion. However, the grindingstone section 3 may be composed of one type grinding stone.

[0027] This embodiment adopts a grinding stone in which vitrified bond(V) or resinoid bond (B) is used, the degree of bonding of which islower than that of metal bond (M) such as cast iron bond, Ni bond or Cubond. The reason is that the abrasive grains easily come off when thegrinding stone is given an overload, so that the polished surface can beprevented from being damaged.

[0028] Next, referring to FIGS. 4A to 4E, explanations will be made intopolishing of the notch portion 21 of the semiconductor wafer 2 in whichthe polishing machine for polishing a periphery of a sheet having thegrinding stone shaft tilting mechanism of the present invention isutilized. The semiconductor wafer 2 is held by a well known chuck notshown in the drawing and rotated, for example, at the rotating speed of1 to 2 rpm. On the other hand, the grinding stone section 3 attached tothe spindle 4 is rotated at a high rotating speed, for example, at therotating speed of 2500 rpm in the same rotating direction as that of thesemiconductor wafer 2 or in the direction reverse to that of thesemiconductor wafer 2.

[0029]FIG. 4A is a view showing a polishing state in which the grindingsection 3 is going to approach the notch portion 21 of the semiconductorwafer 2. The shaft of the spindle 4, which is a rotary shaft of thegrinding stone section 3, is tilted with respect to the rotary shaft ofthe semiconductor wafer 2 by the angle θ. That is, the grinding stonesection 3 is tilted by the angle θ in the tangential direction of thesemiconductor wafer 2. This tilting angle θ is set at a predeterminedangle according to the chamfering angle or the size of the wafer. Inthis case, the grinding stone section 3 is tilted in such a manner thatthe grinding stone section 3 is perpendicular to the center line D whichconnects the rotational center A of the semiconductor wafer 2 with therotational center B of the grinding stone section 3 on a plane parallelwith the plane of the semiconductor wafer 2. Point C is obtained when apoint, at which a portion polished by the groove bottom section 31 b ofthe grinding stone section 3 comes into contact with an outercircumferential line of the semiconductor wafer 2 on the opposite side,is projected on the rotary shaft center B of the grinding stone 3.

[0030] In the above polishing state, when the grinding stone section 3approaches the curvature section R of the wafer in which the outercircumferential section of the semiconductor wafer 2 shifts to the notchportion 21, while the above tilting angle θ, which is perpendicular tothe tangential direction, is being maintained, the grinding stonesection 3 conducts polishing (chamfering) on the curvature section Rwhile the tilting direction of the grinding stone section 3 is beingchanged. Then, polishing is conducted on the outward side of the notchportion 21 as shown in FIG. 4B. In this case, the grinding stone section3 is moved in the directions of X and Y by a moving mechanism not shownso that the grinding stone section 3 can be moved along the linearoblique section of the notch portion 21. Alternatively, thesemiconductor wafer 2 is rotated and moved in the direction Y.

[0031] As shown in FIG. 4B, in this polishing process on the outwardside of the notch portion 21 of the semiconductor wafer 2, according tothe polishing angle of the notch portion 21, while the above tiltingangle θ is being maintained, the tilting of the grinding stone section 3is changed so that the tilting direction can be tilted to a directionparallel to the polishing face (chamfering face) from a directionperpendicular to the center line D.

[0032] As shown in FIG. 4C, in the polishing process of polishing thebottom portion of the notch portion 21 of the semiconductor wafer 2,according to the change in the chamfering direction, the tiltingdirection of the grinding stone section 3 is changed in a reversedirection while the above tilting angle θ is being maintained.

[0033]FIG. 4D is a view showing a polishing state on the inward side ofthe notch section 21. This polishing state is the same as that shown inFIG. 4B. Concerning the tilting of the grinding stone section 3, theabove tilting angle θ is maintained, and the tilting direction is tiltedto parallel to the polishing face of the wafer.

[0034]FIG. 4E is a view showing a state in which the notch portion 21has been polished and the grinding stone section 3 arrives at the outercircumferential section of the semiconductor wafer 2 again. In the samemanner as that of the polishing of the curvature section R on theoutward side, while the grinding stone section 3 is maintaining theabove tilting angle θ, the tilting direction is being changed, and thegrinding stone section 3 polishes the curvature section R in which thenotch portion 21 shifts to the outer circumferential section. Then, thegrinding stone section 3 conducts polishing of the outer circumferentialsection.

[0035] In this case, the tilting direction is perpendicular to thecenter line D described before. The notch portion 21 of thesemiconductor wafer 2 is polished as described above. In order tochamfer the reverse side of the semiconductor wafer 2, the height of theposition of the semiconductor wafer 2 or grinding stone section 3 may beadjusted so that an oblique face opposed to the groove 31 of thegrinding stone section 3 can be used.

[0036] In the case of the semiconductor wafer 2 having anorientation-flat marking portion not shown in the drawing, polishing canbe performed in the manner described above. As another embodiment,polishing can be performed in the following manner. When polishing workarrives at the orientation-flat marking portion, while the tilting angleθ and the tilting direction of the grinding stone section 3 are beingmaintained, the orientation-flat marking portion may be polished so thatthe semiconductor wafer 2 or grinding stone section 3 can be linearlymoved. In this case, rotation of the semiconductor wafer 2 is stoppedand the grinding stone section 3 is kept being rotated.

[0037] As another embodiment of polishing the orientation-flat markingportion, while the tilting angle θ of the grinding stone section 3 isbeing maintained, the orientation-flat marking portion may be polishedso that the tilting direction can be changed in a reverse direction atthe center of the orientation-flat marking portion.

[0038] In this connection, in the grinding stone tilting mechanism usedfor the embodiment of the polishing machine for polishing a periphery ofa sheet of the present invention, a means (linear bearing) for changingthe tilting angle of the spindle 4, which is a grinding stone shaft, anda means (curvature type bearing) for changing the tilting direction arecomposed of different bearings. However, as shown in FIGS. 5A and 5B,both the tilting angle and the tilting direction can be changed by usingone bearing. This can be realized when a spherical linear motor bearing11, the profile of which is formed semispherical, is used. Thisspherical linear motor bearing 11 includes: a semispherical magnet 12having an inverse-cone-shaped opening 13, both sides of which are cutoff so that the spindle 4 holding the grinding stone section 3 canpenetrate and tilt; and a magnetic body 14, the lower face of which isspherical, pivotally holding the spindle 4 and capable of rotating andsliding on spherical surface of the magnet 12. This spherical linearmotor bearing 11 is driven by an electric drive means not shown in thedrawing. In this connection, it is possible to use a spherical bearing,the profile of which is the same, and drive it by a mechanical drivemeans.

[0039] As explained above according to the polishing machine forpolishing a periphery of a sheet of the present invention, the grindingstone shaft tilting mechanism can change not only a tilting angle, bywhich the grinding stone shaft is tilted with respect to the rotaryshaft of the semiconductor wafer, but also its tilting direction.Therefore, even a sheet having a recess portion and protrusion portionin the periphery edge can be accurately chamfered and polished.

[0040] In this connection, although the specific embodiment of thepresent invention is described above in detail, variations andmodifications may be made by one skilled in the art without departingfrom the spirit and scope of the present invention.

1. A polishing machine for polishing a periphery of a sheet in which thesheet having a recess portion or protrusion portion in the periphery isrotated, a rotating grinding stone is made to come into contact with theperiphery of the sheet so as to polish the periphery and the recessportion or protrusion portion, the polishing machine comprising agrinding stone shaft tilting mechanism capable of changing a tiltingangle of a rotary shaft of the grinding stone in the tangentialdirection of the periphery of the sheet and also capable of changing itstilting direction.
 2. A polishing machine for polishing a periphery of asheet according to claim 1, wherein the tilting angle of the grindingstone is adjusted by the grinding stone shaft tilting mechanismaccording to a necessary chamfering angle of the sheet.
 3. A polishingmachine for polishing a periphery of a sheet according to claim 1,wherein the tilting direction of the rotary shaft of the grinding stoneis adjusted according to the rotary angle of the sheet when the recessportion or protrusion portion in the periphery of the sheet is polished.4. A polishing machine for polishing a periphery of a sheet according toclaim 2, wherein the tilting direction of the rotary shaft of thegrinding stone is adjusted according to the rotary angle of the sheetwhen the recess portion or protrusion portion in the periphery of thesheet is polished.
 5. A polishing machine for polishing a periphery of asheet according to claim 1, wherein polishing is conducted while thetilting angle of the grinding stone is being maintained at 0° by thegrinding stone shaft tilting mechanism when a bottom portion of therecess portion of the sheet is polished.
 6. A polishing machine forpolishing a periphery of a sheet according to claim 2, wherein polishingis conducted while the tilting angle of the grinding stone is beingmaintained at 0° by the grinding stone shaft tilting mechanism when abottom portion of the recess portion of the sheet is polished.
 7. Apolishing machine for polishing a periphery of a sheet according toclaim 3, wherein polishing is conducted while the tilting angle of thegrinding stone is being maintained at 0° by the grinding stone shafttilting mechanism when a bottom portion of the recess portion of thesheet is polished.
 8. A polishing machine for polishing a periphery of asheet according to claim 1, wherein an oblique angle of the polishingface of the grinding stone is the same as the oblique angle of theoblique face of the grinding stone groove which is self-formed accordingto the tilting angle of the grinding stone having a groove.
 9. Apolishing machine for polishing a periphery of a sheet according toclaim 1, wherein the degree of bonding of the grinding stone is lowerthan that of a metal bond.
 10. A polishing machine for polishing aperiphery of a sheet according to claim 1, wherein the sheet is asemiconductor wafer and the recess portion is a notch portion ororientation-flat marking portion.